In an image forming apparatus, a developing unit is generally disposed in the neighbourhood of a photosensitive drum for some functional reasons. Such an image forming apparatus is usually provided with a retracting mechanism for retracting the developing unit from its position close to the photosensitive drum in order to avoid damage caused by the contact of the developing unit with the photosensitive drum when replacement or check of the expendable photosensitive drum is carried out. When removing the developing unit from the image forming apparatus, it is also essential to provide a retracting mechanism in view of the above point.
A conventional retracting mechanism is shown in Figures 8 to 10. In the first example shown in FIG. 8, a fixed frame 102 is disposed adjacently to a photosensitive drum 101 and on the upper face of the fixed frame 102 is provided a developing unit supporting carrier 104 which can be moved in the direction (indicated by the arrow A) perpendicular to the axis of the photosensitive drum 101 by turning movement of wheels 103. The movement of the supporting carrier 104 is carried out in such a way: a shaft 105 disposed in the fixed frame 102 is pivoted about a specified angle in the direction indicated by the arrow B against the elastic force of a tension spring (not shown) and the inner wall of the supporting carrier 104 is accordingly pressed by cams (not shown) fixedly attached to the shaft 105.
Although the retracting mechanism shown in FIG. 8 has the advantage of having a simple construction since the developing unit supporting carrier 104 is designed to be movable only in the direction perpendicular to the axis of the photosensitive drum 101, the traveling distance of the supporting carrier 104 is considerably short because of the arrangement in which the supporting carrier 104 is pressed by the cams fixed to the shaft 105. This makes it difficult to ensure sufficient space necessary for mounting the developing unit onto the movable supporting carrier 104 or dismounting therefrom, and the mounting/dismounting operations have to be carried out with the developing unit being left in the image forming apparatus, and accordingly, the conventional apparatus has a problem in its operability.
One proposal for overcoming the above problem is such that as shown in FIGS. 9 and 10, there are provided slide rails 106 on the upper face of a fixed frame so as to move relative to the fixed frame in an axial direction of the photosensitive drum 101 (in the case of FIG. 9) or in a direction perpendicular to the axis of the photosensitive drum 101. According to the retracting systems shown in FIGS. 9 and 10, after the supporting carrier 104 has been retracted in the direction of the arrow A from the developing unit set position to a predetermined retraction position by pivoting the shaft 105 in the direction of the arrow B, the slide rails 106 are slid in the direction C perpendicular to the direction A (in the case of FIG. 9) or in the direction D that is the same as the direction A (in the case of FIG. 10), thereby moving the, supporting carrier 104 to a mounting/dismounting position.
With the arrangement in which the retraction position and the mounting/dismounting position are separately established and the mounting/dismounting position is established outside the apparatus, the foregoing problems relating to the space required for mounting/dismounting of the developing unit and the efficiency of mounting/ dismounting operations can be solved. It will be noted that in the case shown in FIG. 9, the mounting/dismounting position for the developing unit is arranged in front of the apparatus in which the mechanism is incorporated whilst the mounting/dismounting position in the case of FIG. 10 is arranged on the side of the apparatus.